Silver reaction channel

The surface of the silver reaction channels was enhanced by means of the oxidation and outgassing reduction (OAOR) process, which relies on oxidation at 250 °C using pure oxygen and subsequent reduction. An increase in surface area by a factor of 2-3 was reached as indicated by chemisorption data. 

The existence of the two reaction pathways to formaldehyde shown in Scheme 2 is documented in principal with the data from Figure 4. At steady state and at atmospheric pressure the contribution of the two reaction channels needs to be shown independently. In Figure 7 a section through the reaction parameter space of electrolytic silver under isothermal conditions is shown. The molar... 

Physical vapor deposition with shadow masks is known for its simplicity for creating defined areas of thin-film catalytic material in microreactors. This technique was used to deposit silver in the reaction manifolds of microreactors for small-scale synthesis of valuable fine chemicals (Figure 1.4a). The manifolds consisted of a network of 16 parallel channels (19 mm x 600(im x 60-220 tm), in which the oxidative dehydrogenation of 3-methyl-2-buten-l-ol to aldehyde was carried out successfully for temperatures up to 464 °C [31]. The conversion increased smoothly with temperature and low oxygen and high alcohol concentrations were beneficial for selectivity, in addition to less deep channels (higher catalyst surface area to reaction channel volume). For temperatures >400°C, the selectivity deteriorated due to CO and CO2 formation. 

High-temperature experiments have been carried out by Lyon (1976), Silver et al (1980), Silver (1981), Roose et al (1981), and Roose (1981). Lyon conducted flow tube reactor experiments at 1255 K in NO/NH3/ 02/He mixtures, and measured NO, NO2, and NH3 at fixed reaction time with variable NH3/NO ratios. His observations were consistent with a simple six-reaction model including both reaction channels (1) and (2) with... 

Silver attempted to determine the product distribution of the reaction using mass spectrometry and fluorescence techniques (for OH and H). Mass spectrometric data at 300 K indicated that 50-70% of the reactions produce N2 + H2O directly, while OH data (also at 300 K) suggested that 50 30% of the reactions produce OH. Taken together, in the context of a model with reaction channels (1) and (2), the data are consistent with a in the range 0.3-0.5. The fact that no H atoms were observed, however, raises prospects for another reaction channel, possibly N2H -h OH, as suggested by Miller et al (1981), although no N2H was observed in the mass spectrometer data and there is reason to believe N2H should decompose in the exhaust gas stream to N2 + H. 

The overall rate constant = kj -h /c2 + 3) was determined from the measured NH2 concentration and the rate of removal of NO, with the result shown in Fig. 18a. Although the magnitude of is in reasonable agreement with Silver s high-temperature data, the observed activation energy is quite different, suggesting a change in the dominant reaction channel. 

The concentration of silver nanoparticles and ions in solntions was determined by neutron activation analysis [15]. Samples were irradiated in the nuclear reactor at the Institute of Nuclear Physics, Tashkent, Uzbekistan. The product of nuclear reaction ° Ag(n,y)" Ag has the half-life Tj j=253 days. The silver concentration was determined by measnring the intensity of gamma radiation with the energy of 0.657 MeV and 0.884 MeV emitted by "" Ag. A Ge(Li) detector with a resolution of about 1.9 keV at 1.33 MeV and a 6,144-channel analyzer were used for recording gamma-ray quanta. 

The reaction can be run in a minireactor with a silver catalyst in etched channels.15 However, neighbors to the Rhone-Poulenc plant in Institute, West Virginia are still concerned about the 250,000 lb of methyl isocyanate stored there.16... 

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